The need to increase the capacity of data communications networks has led to the development of high-speed and high-capacity fiber optic based network systems. One of the major fiber optic network standards that has emerged in recent years is the Synchronous Optical Network or SONET system. SONET has developed into a high bit-rate fiber optic based transport system that provides the foundation for linking high-speed network switches and multiplexers. It is an intelligent system that provides advanced network management and a standard optical interface.
A SONET network is generally laid out in a ring architecture in which two or more transmission paths over fiber optic cables are provided between network nodes to form a closed loop. Time division multiplexing (TDM) is used to send multiple data streams simultaneously over the transmission paths. Traffic transmitted over a SONET ring may include standard synchronous data (e.g., DS1, DS3), Asynchronous Transfer Mode (ATM) data, and various types of packet data, such as IP (Internet Protocol) data and Frame Relay (FR) data.
SONET networks generally use a paired counter-rotating ring architecture to provide redundancy and protection against transmission failures. Defects or failures on a SONET ring can occur due to several causes, including defects in the fiber optic cable itself, problems in the network elements (nodes), or failures in the processing of a transmitted or received signal. Multiple protection mechanisms are defined for SONET. The most common protection systems are 1+1/1:1 (Bellcore GR-253-CORE), UPSR (Bellcore GR-1400-CORE) and BLSR (Bellcore GR-1230-CORE). ATM standards specify a different set of protection mechanisms. These mechanisms sometimes work in conjunction with the dedicated SONET protection mechanisms or independently of the SONET protection mechanism. SONET rings typically comprise one or more pairs of working rings and standby (or protection) rings. If a working link fails, the bandwidth capacity of the standby link is utilized. Specific mechanisms for monitoring, protecting, and recovering other types of traffic such as Frame Relay or IP are generally dictated by the network administrators or equipment manufacturers for systems that implement this type of traffic. Thus, various levels or layers of protection are provided for network traffic that is transmitted over a SONET ring.
Data is transmitted over a SONET ring in a sequence of synchronized frames. Each frame has a fixed bandwidth or transmission rate (expressed in Mbits per second), depending upon the electrical and optical characteristics of the circuitry implemented in the network elements in the ring. The bandwidth between each pair of nodes along a link is fixed, due to maximum allowable data rates provided by the SONET protocol. Although, in certain cases, it is possible to reallocate or distribute unused bandwidth among links in a SONET ring, such reallocation of bandwidth is typically performed without regard for the level of protection provided. Because of this limitation, bandwidth utilization in SONET rings is typically not optimized for the type and size of data messages transmitted over the networks in relation to the protection of mechanisms used.
Data traffic that utilizes only a fraction of the available bandwidth effectively occupies as much network space and traffic that utilizes the entire bandwidth of a data link in a SONET network. Moreover, similar bandwidth utilization and protection schemes are provided for all of the various types of traffic that can be transported over a SONET network. In the present state SONET network systems, no provision is generally made to optimize protection levels and bandwidth utilization depending upon the amount and type of traffic transmitted over the network. Therefore, present SONET network systems typically do not advantageously allocate bandwidth based upon the type or size of traffic transmitted.